| Abstract: | Photochemistry of Aminoketones. V. Diastereoselective Synthesis of 3-Aryl-azetidin-3-ols via Photocyclization of Aryl-α-amidoalkyl-ketones N-Acyl-azetidin-3-ols 3 and 4 are formed by diastereoselective cyclization of n,π*-excited N-benzyl-N-phenacyl-amides 1 and 2 in ether solution. Dependent on the nature of the p-and α-substituents of the phenacyl part and especially of the N-acylgroups in the amides 1 and 2 competing reactions occur, particularly the NORRISH II cleavage and an oxydative cleavage of the intermediate hydroxybiradicals A . N-Acylgroups with low energy barrier ΔG≠ of internal rotation favour the diastereoselective photocyclization by intramolecular interaction between the amide oxygen atom and the n,π*-CO-group in 1 *, 2 * and the OH group in the biradicals A , respectively. An intramolecular hydrogen bonding enables the N-tosyl-azetidinols 3 to rearrange to the N-tosylamino-methyl-benzhydryl-ketones 6 by 1 -sensitized photoreaction. |
